Automotive construction machine, as well as lifting column for a construction machine

ABSTRACT

Disclosed is an automotive road construction machine, particularly a recycler or a cold stripping machine, comprising an engine frame that is supported by a chassis, a working roller which is stationarily or pivotally mounted on the engine frame and is used for machining a ground surface or road surface. The chassis is provided with wheels or tracked running gears which are connected to the engine frame via lifting column and are vertically adjustable relative to the engine frame. Each individually vertically adjustable lifting column is equipped with a device for measuring the actual vertical state of the lifting column.

BACKGROUND OF THE INVENTION

The invention relates to an automotive construction machine, as well asa lifting column for a construction machine.

Such construction machinery is known, for instance, from DE 103 57 074B3. The said construction machine shows a machine frame that issupported by a chassis, as well as a working drum that is mounted at themachine frame in an immovable and/or pivotable manner, and is used forworking a ground surface or traffic surface. The chassis is providedwith wheels and/or crawler track units which are connected to themachine frame via lifting columns and are individually adjustable inheight relative to the machine frame.

The adjustment in height is made possible by a controller that raises orlowers the lifting columns by controlling the hydraulic input orhydraulic discharge of piston cylinder units in the lifting columns.

The construction machine described in DE 103 57 074 B3 is a recycler,and the disclosure of this publication is included in the presentapplication to the extent that it is related to recyclers.

A chassis for a machine used for milling carriageway pavements is knownfrom DE 196 17 442 C1, the front axle of the said chassis being, forinstance, adjustable in height in the manner of a full-floating axle.The lifting columns of the chassis are capable of being raised orlowered respectively in a reciprocally opposed manner. The disclosure ofthis publication is also included by reference into the presentapplication.

A known construction machine of the applicant is the recycler WR 2000,the wheels of which are connected to the machine frame via liftingcolumns that are adjustable in height hydraulically. Each wheel isdriven by an own hydraulic motor. The known construction machine isequipped with all-wheel steering, with the front and/or the rear wheelsbeing capable of acting as the steered axle.

It is understood that the present application is not limited towheel-driven construction machines, but also includes such constructionmachines that are provided with crawler track units or a mixture ofwheels and crawler track units.

In the known construction machines, the lifting columns are adjustedmanually via switchover valves, with sensors detecting that the pistonof the piston cylinder unit adjusting the lifting column has reachedpre-determined positions. The sensors may detect, for instance, theupper edge of the piston in the piston cylinder unit. A first sensordetects the position of the piston in an operating position for milling,and a further sensor detects the position of the piston in a transportposition. In operating position, the machine frame therefore always hasthe same, pre-determined distance from the ground surface. When thepiston has left the pre-defined sensor positions, the information aboutthe position of the machine is lost. It is, in particular, not possibleto adjust any other operating positions in a flexible manner withoutremounting the position sensors. It is not even possible to, forinstance, adjust an operating position that is parallel to thepre-adjusted operating position but deviates from the same in height.What is more, it is not possible to adjust a defined transverseinclination or any other practical position of the machine frame or themachine respectively without cumbersome remounting efforts.

This creates the additional problem that the machine frame can adopt adifferent distance to the ground surface or traffic surface because ofdifferent loads or load distributions which are due to, for instance, adifferent filling level of the fuel tank or a water tank.

In case of wheels, deviations additionally result because of the fillingpressure, the temperature and the interaction of the relatively softwheel with the ground surface or traffic surface, which may, forinstance, cause an alteration in distance of several centimeters. Thesealterations in distance of the machine frame relative to the groundsurface require the position of the sensors to be displaced. Even thoughit is also possible to unlock the sensor for the operating position andto override this lifting position, the disadvantage results that thepiston, at its front surfaces, touches the respective front surfaces ofthe cylinder when the mechanical limit stop of the piston cylinder unithas been reached, which may cause the piston of the piston cylinder unitto turn loose when carrying out steering movements of the wheels.

The purpose of the invention is to avoid the aforementioneddisadvantages and to enable the vehicle driver to select any givenlifting position of the lifting columns as operating position inparticular for the working operation.

The invention provides in an advantageous manner that each individualheight-adjustable lifting column is provided with a measuring device formeasuring the current lifting state of the lifting column, the liftingcolumns comprise two hollow cylinders capable of telescoping which serveas guiding unit and accommodate at least one piston cylinder unit forheight adjustment, preferably in a coaxial manner, on their inside, thateach individual height-adjustable lifting column is provided with ameasuring device for measuring the current lifting state of the liftingcolumn, the measuring device is coupled with elements of the liftingcolumn, which are adjustable relative to one another in accordance withthe lifting position, in such a manner that a path signal pertaining tothe lifting position of each lifting column is continuously detectableby the measuring device, and that a controller receiving the measuredpath signals from the measuring devices of all the lifting columnsregulates the lifting state of the lifting columns in accordance withthe measured path signals of the measuring devices and/or theiralteration over time.

The invention provides in an advantageous manner for pre-selectablepositions of the lifting columns to be adjusted in a regulated manner,permitting the use of the measured path signal, and of the velocity andacceleration signals which can be deduced therefrom. Recording of themeasured values enables the lifting state of the lifting columns to beregulated automatically. A controller receiving the measured signalsfrom the measuring device can adjust a desired lifting position of thelifting columns in a regulated manner without overshooting or with aslittle overshooting as possible in accordance with the measured signalsof the measuring device and/or their alteration over time.

The measured signals may be suitable for supplying to an indicatordevice for the lifting position of the lifting columns. Because thevehicle driver receives information on the current lifting state of eachlifting column via the indicator device, it is possible to adjust anddefine as operating position a freely selectable position of the machineframe without the need for limit switches or sensors to be displaced.Hence, the vehicle driver has the possibility to equalize different loadsituations that may arise due to, for instance, a different fillinglevel of the fuel tank or the water tank. Furthermore, influences of therelatively soft wheels due to different temperatures, a differentfilling pressure or because of the interactions with the ground can beequalized individually for each wheel or crawler track unit.

The measuring device for the lifting position preferably includes a pathmeasuring device, and all known path measuring systems like, forinstance, capacitive, inductive, mechanical path measuring systems orlaser measuring systems may be used.

The lifting columns comprise two hollow cylinders capable of telescopingwhich serve as guiding unit and accommodate at least one piston cylinderunit, preferably in a coaxial manner, on their inside.

A preferred path measuring device includes at least one wire-rope thatis coupled with the elements of a lifting column, and one wire-ropesensor.

A wire-rope that is under tension and capable of being rolled up iscoupled with elements of the lifting column, which are capable of beingdisplaced relative to one another in accordance with the liftingposition, in such a manner that a path signal pertaining to the liftingposition of each lifting column is detectable continuously. The pathsignal transmitted to the indicator device may be used for manualcontrol of the height adjustment by the vehicle driver with the aid ofthe indicator device, but also for automatic control or regulation.

The construction machine can be adjusted to a reference plane, where adesired spatial position like, for instance, a parallel position of themachine frame to the ground surface or traffic surface can be stored onthe reference plane by storing the current measured signals of themeasuring device in accordance with the current lifting positions of thelifting columns as a reference lifting position of the chassis.

By means of the reference plane, which is preferably a horizontal plane,the vehicle driver can bring the machine frame into a specific positionwhich he can define as the reference lifting position. In case of alevel machine frame, the said machine frame could, for instance, bebrought into a precisely horizontal position which, with apre-determined distance from the ground or the traffic surface, could bedefined as the reference lifting position of the lifting columns. Thevehicle driver can recognize the said reference lifting position bymeans of the indicator device and can approach it specifically as andwhen required. On the other hand, it is also possible to raise or tolower individual lifting columns or a combination of lifting columns bya specific amount. The vehicle driver can, for instance, also adjust anoperating position which deviates from the reference lifting position bya specific amount, e.g. 100 mm, or a specific transverse inclination ora plane in space arbitrarily defined by the vehicle driver.

In a preferred embodiment, it is provided that at least one limitingvalue for the height adjustment monitored by the measuring device isadjustable for each lifting column, the said limiting value limiting thelowest and/or highest lifting position of a lifting column to apre-determined position. It is thus ensured that the piston cylinderunit provided on the inside of a lifting column will not run up againstits corresponding mechanical limit stops, as the piston cylinder unitmay be damaged or may turn loose from the lifting column in thesemechanical end positions, in particular in case of steering angles.

Consequently, it is provided that the lowest or highest lifting positionin the direction of movement is positioned in front of the mechanicallimit stop of the piston against the cylinder of the piston cylinderunit.

Recording of the measured values enables a controller, which receivesthe measured signals from the measuring devices, to regulate the liftingstate of the lifting columns automatically in such a manner that themachine frame is subject to the smallest possible displacement due tothe structure of the ground surface or traffic surface.

Alternatively, it is also possible for the controller to regulate thelifting state of the lifting columns by means of the measured signals insuch a manner that the machine frame is subject to the smallest possibletransverse inclination or transverse oscillation transverse to thedirection of travel due to the existing structure of the ground surfaceor traffic surface.

It may additionally be provided that, when altering the lifting state ofone wheel or crawler track unit, a neighbouring wheel or crawler trackunit in transverse direction or longitudinal direction of the machineframe is adjustable in height in an opposite manner. Controlling of thelifting state may be effected, for instance, in accordance with thehydraulic method described in DE 196 17 442 C1. In case of a hydraulicforced coupling of neighbouring lifting columns, one single measuringdevice for both lifting columns is sufficient due to the identicalamount of stroke adjustment.

There is, however, also the possibility of controlling the lifting stateof each wheel purely electronically in the manner of a full-floatingaxle. With such a full-floating control, an additional stroke adjustmentcan be overridden by the vehicle driver.

With the reciprocal control of the lifting state, the neighbouringwheels or crawler track units are preferably adjusted in height by thesame amount and in an opposite manner.

In case of a cold milling machine, the rear wheels or crawler trackunits when seen in the direction of travel are preferably adjustable inheight in the manner of a full-floating axle by the same amount and inopposite direction.

In case of a recycler, the wheels or crawler track units arranged behindone another on one side of the machine when seen in the direction oftravel may be adjustable in height in the manner of a full-floating axleby the same amount and in opposite direction.

A controller receiving the measured signals from the measuring devicescan adjust a desired lifting position of the lifting columns withoutovershooting or with as little overshooting as possible in accordancewith the measured signals from the measuring devices and/or theiralteration over time.

The measured signals from the measuring devices may be calibrated to aunit of length, so that a specified stroke amount can be entered inmillimeters for the purpose of height adjustment.

The controller may regulate the working depth of the working drum, inwhich case the controller receives the measured path signals from themeasuring device and includes them into the regulation of the workingdepth of the working drum.

Each lifting column is provided at the lower end with a support for thewheel or crawler track unit, where a distance sensor measures thedistance of the support to the ground surface and traffic surface,preferably in a pre-determined distance in front of or next to the wheelor crawler track unit, and transmits a measured signal to a controllerfor the lifting position of the lifting columns, and/or to a controllerfor the working depth of the working drum, and/or to the indicatordevice.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the following, embodiments of the invention are explained in moredetail with reference to the drawings. The following is shown:

FIG. 1 is a side view of the construction machine in accordance with theinvention, in which the working drum is in a working position,

FIG. 2 a top view of the construction machine in accordance with FIG. 1,and

FIG. 3 a lifting column of the construction machine.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a road construction machine 1 for producing and workingcarriageways by stabilizing insufficiently stable soils or by recyclingroad surfaces, with a machine frame 4 supported by a chassis 2, as it isbasically known from DE 103 57 074 B3. The chassis 2 is provided withtwo each rear and front wheels 10, which are attached to lifting columns14 in a height-adjustable manner and can be raised and loweredindependently of one another or also synchronously to one another. It isunderstood that other drive means like, for instance, crawler trackunits may also be provided in lieu of the wheels 10. The wheels orcrawler track units may also be referred to as ground engaging supportsfor supporting the construction machine on the ground surface or trafficsurface 24. The lifting columns 14 are attached to the machine frame 4.

Both axles of the chassis, which are formed by the front and rear wheels10 respectively, may be steerable.

As can be seen from FIGS. 1 and 2, an operator's platform 12 for avehicle driver is arranged at the machine frame 4 above the front wheels10 or in front of the front wheels 10, with a combustion engine 32 forthe travel drive and for driving a working drum 6 being arranged behindthe driver. In this manner, the operator's platform 12 can beergonomically optimized for the vehicle driver.

The working drum 6 which rotates, for instance, in opposition to thedirection of travel when seen in the direction of travel, and the axisof which extends transversely to the direction of travel, is mounted topivot relative to the machine frame 4 in such a manner that it iscapable of being pivoted from an idle position to a working position, asdepicted in FIG. 1, by means of pivoting arms 42 arranged on both sides.Each pivoting arm 42 is mounted in the machine frame 4 at one end andaccommodates the support of the working drum 6 at its other end.

It is also possible to operate the machine 1 in reversing direction,with the milling operation then taking place synchronously to thedirection of travel.

The working drum 6 is, for instance, equipped with cutting tools thatare not depicted in the drawings in order to be able to work a groundsurface or traffic surface 24.

The working drum 6 is surrounded by a hood 28 which, as can be seen fromFIG. 1, is capable of being raised together with the working drum 6 bymeans of the pivoting arms 42.

In operating position, the hood 28 rests on the ground surface ortraffic surface 24 to be worked, as can be seen from FIG. 1, while theworking drum 6 is capable of being pivoted further down according to themilling depth.

It is understood that other embodiments of such a construction machineexist in which the hood 28, or the hood 28 and the working drum 6, aremounted at the machine frame 4 in a rigid manner. In the latter case,the working depth of the working drum 6 is adjusted via the liftingcolumns 14, in all other cases through an adjustment in height of theworking drum 6.

FIG. 3 shows an individual lifting column 14 comprising two hollowcylinders 13, 15 which are capable of telescoping in a form-fittingmanner. The hollow cylinders 13, 15 serve as guiding unit for the heightadjustment of the machine frame 4. The upper outer hollow cylinder 13 isattached at the machine frame 4, and the lower inner hollow cylinder 15is attached at a support 11 which may be coupled with a wheel 10 or acrawler track unit. The lifting column 14 is further provided with ahydraulic piston cylinder unit 16 for the stroke adjustment. The pistoncylinder unit 16 acts between the machine frame 4 and the support 11, sothat the machine frame 4 is capable of being adjusted in height relativeto the support 11 and thus, ultimately, relative to the ground surfaceor the traffic surface 24 respectively. In the embodiment shown in FIG.3, the piston element of the piston cylinder unit 16 is attached at thesupport 11, and the cylinder element of the piston cylinder unit 16 isattached at the upper hollow cylinder 13, which is attached at themachine frame 4.

It is understood that more than one piston cylinder unit 16 may also bepresent in the lifting column 14.

The piston cylinder unit 16 may also be force-coupled hydraulically witha neighbouring lifting column 14, as has been basically described in DE196 17 442 C1, in order to form a purely hydraulic full-floating axle.

The lifting column 14 is provided with a measuring device 18 formeasuring the current lifting state of the lifting column 14. In theembodiment, the said measuring device 18 includes a wire-rope 22 that isattached at the support 11 or the lower hollow cylinder 15 and is, onthe other hand, coupled with a wire-rope sensor 21 that is attached atthe cylinder element of the piston cylinder unit 16 or at the upperhollow cylinder 13. The stroke path of the lifting column 14 can bemeasured by means of the wire-rope sensor 21. The wire-rope sensor 21,and the path signal produced by the same, is ultimately also suitablefor being converted into a velocity signal or acceleration signal byincluding a time measurement.

The measured path signal of the wire-rope sensor 21 is transmitted to anindicator device 20 and/or a controller 23 by means of a signal line 26.The indicator device 20 and/or the controller 23 receive measured pathsignals from each lifting column, as indicated in the drawing in FIG. 3.With a total of four existing lifting columns 14, four measured pathsignals can be displayed in the indicator device 20, so that the vehicledriver is immediately informed about the current lifting state of eachlifting column and can alter the lifting position, if required.

The measured path signals can additionally be supplied to a controller23, which enables overall control or regulation of the lifting positionof the lifting columns 14.

The controller 23 can, for instance, adjust a desired lifting positionof the lifting column 14 without overshooting or with as littleovershooting as possible in accordance with the measured path signals ofthe measuring devices 18 and/or their alteration over time.

In case of a full-floating axle, floating can be effected purelyhydraulically through piston cylinder units 16 which are provided with apiston capable of being loaded from two sides, and the counter-operatingcylinder chambers of which are force-coupled with the correspondingcylinder chambers of the piston cylinder unit of a neighbouring wheel10. Alternatively, a height adjustment in the manner of a full-floatingaxle may be effected with purely electronic control by means of themeasured path signals detected.

The control or regulation may be such that, for instance, the machineframe 4 is subject to the smallest possible displacement.

The machine frame 4 may alternatively be regulated by means of thelifting state of the lifting columns 14 in such a manner that apre-determined transverse inclination of the machine frame 4 transverseto the direction of travel is maintained.

A further alternative provides that the time sequence of the position ofthe machine frame 4 such as, for instance, a path-dependent transverseinclination sequence of the machine frame 4, may also be regulated bymeans of the measured path signals and the piston cylinder units 16 incombination with a path or machine position measurement.

Ultimately, it is also understandable that a longitudinal inclination ora combination of a transverse and longitudinal inclination can also beregulated by means of the controller 23.

The measured signals of the measuring device 18 may be calibrated to aunit of length like, for instance, millimeters. In this way, it ispossible for the vehicle driver to also alter the lifting state of thelifting columns 14 through entering a specific stroke in millimeters.

Each lifting column 14 may be provided with a distance sensor 30 each atthe supports 11, which measures the distance of the support 11 to theground surface and traffic surface 24. By means of the measured signalof the distance sensors 30, and in combination with the measured pathsignals of the measuring device 18, the controller 23 for the liftingcolumns 14 can also calculate the current distance of the machine frame4 from the ground surface and traffic surface 24.

The distance sensor 30 can measure the distance of the support 11 to theground surface and traffic surface 24 also in a pre-determined distancein front of or next to the wheel 10 or crawler track unit. Measuring infront of the wheel 10 offers the possibility of using the measuredsignal of the distance sensor 30 for the purpose of controlling theheight adjustment of the lifting columns 14 in a manner that allows animmediate reaction to any ground irregularity. Finally, the distancesensors 30 are also capable of supplying measured signals for aregulation of the milling depth, where the measured signals of thedistance sensors 30 and the measured path signals of the measuringdevice 18 are evaluated on a joint basis.

Although a preferred embodiment of the invention has been specificallyillustrated and described herein, it is to be understood that minorvariations may be made in the apparatus without departing from thespirit and scope of the invention, as defined by the appended claims.

What is claimed is:
 1. A road construction machine, comprising: amachine frame; a working drum supported from the machine frame forworking a ground surface or traffic surface; a plurality of groundengaging supports for supporting the construction machine on the groundsurface or traffic surface; a plurality of lifting columns, each one ofthe lifting columns being connected between the machine frame and one ofthe ground engaging supports, each one of the lifting columns includingtwo telescoping hollow column members and at least one piston cylinderunit located within the telescoping hollow column members for adjustinga height of the lifting column so that each one of the lifting columnsis adjustable in height relative to the machine frame, each liftingcolumn having a lifting position corresponding to a position of one ofthe two telescoping hollow column members relative to the other of thetwo telescoping hollow column members; and a plurality of liftingposition sensors, each lifting position sensor being coupled withelements of one of the lifting columns, which elements are capable ofbeing displaced relative to one another in accordance with the liftingposition of the lifting column in such a manner that a signal includinginformation on a current lifting position of the lifting column isproduced by the lifting position sensor, wherein each of the liftingposition sensors is connected to the at least one piston cylinder unitlocated within its associated lifting column.
 2. The road constructionmachine of claim 1, further comprising: a controller configured toreceive the signals from the lifting position sensors, and to regulatethe lifting positions of the lifting columns in response at least inpart to the signals from the lifting position sensors.
 3. The roadconstruction machine of claim 2, further comprising: an indicator deviceoperable to display the lifting positions of each of the lifting columnscorresponding to the signals produced by the lifting position sensors.4. The road construction machine of claim 2, wherein: the controller isconfigured to store the signals from the lifting position sensorscorresponding to current lifting positions of the lifting columns and tothereby define a current spatial position of the machine frame as areference spatial position of the machine frame.
 5. The roadconstruction machine of claim 2, wherein: the controller is configuredto provide at least one limiting value for the height adjustment of eachof the lifting columns.
 6. The road construction machine of claim 5,wherein: the limiting value for the height adjustment preventsengagement of a mechanical limit stop of a piston against a cylinder ofthe piston cylinder unit of each lifting column.
 7. The roadconstruction machine of claim 5, wherein: the limiting value defines apredetermined lifting position of the respective lifting column suchthat the respective piston cylinder unit is not run up against amechanical stop of the piston cylinder unit when the lifting column isin the predetermined position.
 8. The road construction machine of claim2, wherein: the controller is configured to regulate the liftingpositions of the plurality of lifting columns in such a manner that themachine frame has a predetermined transverse inclination relative to theground surface or traffic surface and transverse to a direction oftravel of the machine frame.
 9. The road construction machine of claim8, wherein: the controller is configured to vary the transverseinclination of the machine frame in a pre-determined path-dependenttransverse inclination sequence.
 10. The road construction machine ofclaim 2, wherein: the controller is configured such that with thealteration of the lifting position and height of one of the liftingcolumns, a neighboring lifting column in transverse direction orlongitudinal direction of the machine frame is adjusted in height in anopposite manner.
 11. The road construction machine of claim 10, wherein:the height of the neighboring lifting column is adjusted by the sameamount as the alteration of the height of said one of the liftingcolumns.
 12. The road construction machine of claim 10, wherein: saidone of the lifting columns and said neighboring lifting column areconnected to two front ground engaging supports so that the liftingcolumns associated with front ground engaging supports areheight-adjustable in the manner of a full-floating axle.
 13. The roadconstruction machine of claim 2, wherein: the controller is configuredto reduce overshooting in the regulating of the lifting positions of thelifting columns with reference to desired lifting positions of thelifting columns.
 14. The road construction machine of claim 2, wherein:the controller is configured to calibrate the lifting positions sensedby the lifting position sensors to a unit of length.
 15. The roadconstruction machine of claim 2, wherein: the controller is configuredto regulate a working depth of the working drum at least in part inresponse to the signals produced by the lifting position sensors. 16.The road construction machine of claim 2, wherein: the controller isconfigured to raise the lifting columns synchronously to one another.17. The road construction machine of claim 2, wherein: the controller isconfigured to lower the lifting columns synchronously to one another.18. The road construction machine of claim 2, wherein: the controller isconfigured to move the machine frame from a first frame position to asecond frame position by adjusting the heights of all of the liftingcolumns by equal amounts.
 19. The road construction machine of claim 2,wherein: the controller is configured to bring the machine frame to aframe position parallel to the ground surface or traffic surface withthe machine frame being a predetermined distance from the ground surfaceor traffic surface.
 20. The road construction machine of claim 19,wherein: the frame position parallel to the ground surface or trafficsurface is a horizontal position.
 21. The road construction machine ofclaim 1, wherein: the working drum is fixed in height relative to themachine frame and a working depth of the working drum is adjusted byadjusting the lifting positions of the lifting columns.
 22. The roadconstruction machine of claim 1, further comprising: an indicator deviceoperable to display the lifting positions of each of the lifting columnscorresponding to the signals produced by the lifting position sensors.23. The road construction machine of claim 22, wherein: the plurality oflifting columns includes two front lifting columns and two rear liftingcolumns; and the indicator device is operable to display the liftingpositions of the two front lifting columns and two rear lifting columns.24. The road construction machine of claim 2, wherein: the controller isconfigured to raise and lower the plurality of lifting columnsindependently of one another.
 25. The road construction machine of claim2, wherein: the controller is configured to raise and lower acombination of lifting columns synchronously and by a specific amount.26. The road construction machine of claim 2, wherein: the plurality oflifting position sensors comprises one or more inductive path measuringdevices.
 27. The road construction machine of claim 2, wherein: theplurality of lifting position sensors comprises one or more capacitivepath measuring devices.
 28. The road construction machine of claim 2,wherein: the plurality of lifting position sensors comprises one or moremechanical path measuring devices.
 29. The road construction machine ofclaim 2, wherein: the plurality of lifting position sensors comprisesone or more laser measuring devices.
 30. A road construction machine,comprising: a machine frame; a working drum supported from the machineframe for working a ground surface or traffic surface; a plurality ofground engaging supports for supporting the construction machine on theground surface or traffic surface; a plurality of lifting columns, eachone of the lifting columns being connected between the machine frame andone of the ground engaging supports, each one of the lifting columnsincluding two telescoping hollow column members and at least one pistoncylinder unit located within the telescoping hollow column members foradjusting a height of the lifting column so that each one of the liftingcolumns is adjustable in height relative to the machine frame, eachlifting column having a lifting position corresponding to a position ofone of the two telescoping hollow column members relative to the otherof the two telescoping hollow column members; and a plurality of liftingposition sensors, each lifting position sensor being coupled withelements of one of the lifting columns, which elements are capable ofbeing displaced relative to one another in accordance with the liftingposition of the lifting column in such a manner that a signal includinginformation on a current lifting position of the lifting column isproduced by the lifting position sensor; wherein each of the liftingcolumns includes a lifting column support at a lower end of the liftingcolumn, each lifting column support being attached to one of the groundengaging supports; and further comprising a plurality of distancesensors, one of said distance sensors being attached to each of thelifting column supports and arranged to measure a vertical distance ofthe lifting column support from the ground surface or traffic surface.31. The road construction machine of claim 30, wherein: each of thedistance sensors is located relative to its associated lifting columnsupport, so that the vertical distance is measured at a pre-determinedhorizontal position relative to its associated ground engaging support.32. The road construction machine of claim 30, wherein: the elements ofthe lifting column, which elements are capable of being displacedrelative to one another in accordance with the lifting position of thelifting column, include the at least one piston cylinder unit locatedwithin the lifting column.